Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

502
FXUS63 KLOT 280006
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
606 PM CST Sat Dec 27 2025

.KEY MESSAGES...

- Showers and some thunderstorms likely areawide Sunday into
  early Sunday evening.

- Thunderstorms may pose a locally damaging wind threat Sunday
  afternoon/early evening, mainly south of I-80.

- Very strong winds will usher in drastically colder air Sunday
  night into Monday, with some snow showers possible.

- Chance (40-50%) for light accumulating snow Wednesday
  afternoon into Wednesday evening.

&&

.DISCUSSION...
Issued at 204 PM CST Sat Dec 27 2025

Through Monday:

Early this afternoon, the early stages of lee cyclogenesis are
underway over the central Plains as a series of shortwave
impulses ejects east off the Colorado and New Mexico Rockies.
The lingering baroclinic zone found meandering about the Ohio
and lower Missouri river valleys this morning will serve as the
storm`s warm front. The boundary has begun to gradually scoot
northward as it tags up with the deepening cyclone. It`s
expected to move into our southern CWA early this evening and
continue lifting northward through the night as the low works
into the Midwest. As it does, we should see the area warm by
several degrees, especially in our south, during the late
evening and overnight. Temperatures are progged in the 40s area-
wide at dusk, and up into the mid 40s near the WI state line to
the lower and middle 50s south of I-80 by dawn on Sunday.

Mid level moisture will be lacking ahead of the front, but
there may be enough in the low levels to produce instances of
drizzle this evening amid some noteworthy moist isentropic
ascent ahead of the boundary. An uptick in layer moisture and
forcing look to generate some isolated to widely scattered
showers during the overnight. At least some visibility
reductions are also likely tonight into early tomorrow. The
lowest visibilities are favored immediately along and north of
the surface front, which should roughly equate the areas near
and north of I-80. Any light rain and especially drizzle that
materializes during the night will only increase the dense fog
potential. A targeted Dense Fog Advisory may be in the cards
later tonight as confidence grows.

The low will really begin to intensify during the morning once
the mid level low drops south into the northern Plains and
upper Midwest from Saskatchewan. Every piece of deterministic
guidance has this storm bombing, or getting awfully close to it,
between Sunday and Monday mornings. An impending secondary low
will also inject a plume of rich mid level moisture into the
area early Sunday. Accordingly, expectations are for precip
coverage to expand on either side of the warm front during the
morning, especially the latter part of the morning as the
double-barreled low crosses the Mississippi.

There is increasing concern for a period of training convective
showers along the warm front in the morning. As the low level
jet ramps up south of the warm front, latest RAP guidance
depicts strong low level shearing deformation and frontogenesis
along the boundary. Additionally, deep shear vectors will be
oriented roughly parallel to the boundary and we`ll be seeing
PWATs in excess of 1". This should result in steady moderate to
heavy rain along the boundary. Models have really ramped up this
signal over the past few runs. Some camps are depicting a
marginal amount of low level CAPE lifting north into the area
during the morning as the low levels warm around the front. A
lack of cooler air aloft should place a mid level lid on
parcels, but a few convective cores may grow just deep enough to
produce lightning, especially amid the deep, strong dynamic
forcing. Moreso than lightning though, the bigger concern is for
these mechanisms to stir up bands of heavy rainfall. A small
majority of deterministic camps paint localized areas of 0.5+"
6-hr totals beneath the warm front in our CWA during the
morning, and a couple to a few tenths are possible on a more
widespread basis. A big question is not only where exactly this
front will align, but whether the effective front will be more
stationary and target one corridor or if it`ll be more
transient and distribute the rain over a broader area. If the
former, flooding does not look like a big concern but localized
ponding and flooding of low spots is certainly plausible. WPC
has maintained a marginal risk for excessive rain in our CWA in
part for this warm frontal setup.

The better storm chances, including the severe potential, will
be during the afternoon and early evening along the
strengthening warm conveyor and effective cold front. Guidance
continues to resolve instability that generally wouldn`t raise
many concerns in the warm season, but given the dynamic forcing
associated with this wave and the impressive shear profiles,
marginal instability is likely all we`ll need to stir up
convection. Over the past couple of days now, there`s been a
slight northwestward shift in the heavy rain and thunder
environment for the afternoon and evening. The RAP has
consistently been farther northwest since the storm started
coming into its view yesterday. It even resolves a couple of
hundred Joules of elevated CAPE making it up to our northwestern
CWA. If that materializes, convective showers will be possible
area-wide. However, the more supportive thunder environment,
including the severe threat, still look to favor areas south of
I-80, and even moreso the farther south you go. A strong low
level jet atop the conveyor will provide substantial low level
and deep shear, and vectors will be oriented roughly normal to
the baroclinic zone. This setup will favor an eastward-moving
line of convection across central and southern portions of the
Midwest. With little to no instability available above the
lowest couple of hundred millibars, it`s very possible that we
see little lightning out this line. But the strong flow residing
just off the deck provide an opportunity for strong to locally
damaging winds at the surface. And the veering nature of the
strong low level shear does raise some concern for a non-zero
QLCS tornado threat if the near-surface environment can
destabilize along the leading edge. Again, the severe threat is
primarily for areas south of I-80 and seemingly greater with
south and southeastward extent where the better instability and
kinematics will focus. The line looks to be off to our east by
mid-evening.

Profiles will cool rapidly in the wake of the front Sunday
evening and night, even quicker than previously advertised. This
will bring a quick transition from rain to snow west to east
during the evening. Most will likely see only gusty flurries or
lighter snow showers during much of the night, but better
chances for bonafide snow showers will be found up in our north
where better attendant moisture and forcing will be found.
Chances for snow showers will expand southward around much of
the area for Monday morning as the low swings across the lake.
Greatest chances for accumulations will be north of I-80, but a
dusting will be possible area-wide. More meaningful
accumulations closer to or in excess of an inch may be on tap
for northern locales.

Final thing of note with this system will be the gusty winds
Sunday evening through Monday. Winds look even stronger during
this period than previously thought now that the high-res camps
have come into play. While showers may drag some stronger winds
down to the surface earlier in the day, gusts will really open
up during the evening in the cold advection wing. Confidence is
high in widespread 45 to 50 mph westerly gusts during the back
half of the evening through Monday morning. Occasional gusts to
55 mph will also be possible. Accordingly, decided to hoist an
area-wide Wind Advisory on this shift from Sunday evening
through the end of Monday afternoon. Gusts should ease during
the evening as the system lifts northeast of the Great Lakes.

Doom


Monday Night through Saturday:

Primary forecast concern for the extended is the chance for
light accumulating snow Wednesday afternoon/evening. This has
been a fairly consistent feature in the models for several days
now. A weak clipper system is expected to move across the
region Wednesday night with another push of colder air behind
it. A narrow band of light snow will be possible somewhere
nearby or across the local area, though there remains
considerable spread in the ensembles. Blended guidance has
increased pops, now in the mid/high chance range. Timing also
looks to be a bit faster. If snow does develop, trends would now
support mid/late Wednesday afternoon, then ending overnight,
before daybreak Thursday morning.

Temps perhaps in the upper single digits/lower teens Tuesday
morning with northwest winds still in the 10-15 mph range, could
produce subzero wind chills Thursday morning. Blended guidance
then warmed temps almost every period into the weekend, from
this early morning`s forecast. Some brief moderation in temps
may be possible Wednesday ahead of the clipper, but there
appears to be decent ensemble support for a rather cold New
Year`s Day with high pressure then moving across the area
Thursday night. Should there be a new coating of snow, that may
allow low temps Thursday night to be colder than guidance is
suggesting. But from this distance, made no changes to the
blended guidance.

Temps begin to slowly warm Friday into Saturday with high temps
next Saturday possibly back into the lower/mid 30s ahead of the
next potential weather system that may bring mixed wintry precip
somewhere nearby or to the local area. cms

&&

.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 606 PM CST Sat Dec 27 2025

Aviation forecast concerns:

- Ceilings/visibility lowering through IFR into LIFR tonight
  into Sunday, with drizzle/rain/fog. VLIFR possible, especially
  at DPA/RFD west/northwest of Chicago.

- SHRA expected Sunday with embedded TS and gusty winds
  possible.

- Strong cold front with wind shift to WNW toward evening
  Sunday. Gusts >35 kt likely by late evening. Scattered SHSN
  possible.

Surface low pressure was taking shape along the KS/CO border
early this evening. A broad region of south-southeast low level
flow extends into the Midwest/Great Lakes region ahead of this
developing system. Renewed northward advection of moisture and
eventual development of drizzle/rain tonight will make for a
gradual downward trend in ceiling heights and visibility. IFR
CIGs are already widespread as of 00Z, with LIFR in spots
including KRFD. LIFR (VLIFR potentially especially at RFD/DPA)
is likely later tonight into Sunday as drizzle/rain develops and
further moistens the low level air mass in addition to the rise
in dew points due to advection. Guidance is quite bullish on
potentially VLIFR persisting for many hours into the day Sunday
and even for the Chicago metro terminals and can`t rule this out,
though confidence in this decreases with southeastward extent,
due to the expected track of the low through the Chicago area.
Will continue to monitor, and if that trend becomes more
apparent then a mention of VLIFR CIGs and/or VSBYs may be
warranted, potentially for all sites.

Coverage of SHRA will increase Sunday morning with the approach
of the low and its accompanying mid-level disturbance. These
showers may help to locally improve cigs/vis, though expect that
LIFR to low-end IFR will be the prevailing conditions. There
also remains a potential for embedded TSRA along/south of the
low track, and have maintained a prob30 mention for ORD/MDW and
GYY midday through mid-afternoon when the warm front is nearby.
Storms or heavier convective SHRA may also be able to mix down
gusty mainly southwest winds to 25-30 kts. Greater chances for
higher TS coverage should remain generally southeast of the
I-55/I-80 corridors south and southeast of Chicago proper.

Winds will generally be from the southeast tonight into Sunday
morning, with areas especially just south of the terminals
potentially becoming more south during the day as the low tracks
across the area. Winds will likely become somewhat light and
variable by midday/early afternoon (outside of any stronger
showers or TS) as the low center moves overhead. That will
change rapidly early Sunday evening however, as winds shift
west-northwest and become strong and gusty (possibly in excess
of 35 kts later in the evening) behind the departing low. A
rapid drop in temperatures may also support scattered snow
showers by late evening, potentially with some minor accums
overnight.

Ratzer

&&

.MARINE...
Issued at 256 PM CST Sat Dec 27 2025

A storm watch remains in effect for the Illinois and Indiana
nearshore from Sunday evening through midday Monday. Low
pressure will develop over the central Plains tonight and move
northeast Sunday, deepening rapidly as it moves along the
eastern shore of Lake Michigan and then slowing as it reaches
northern Lake Huron Sunday into Sunday night. A strong cold
front will move across the southern end of Lake Michigan late
Sunday afternoon/early Sunday evening, shifting winds westerly
with speeds/gusts quickly increasing. A few hour period of
gales is expected before the potential storm force winds. With
this time period for storm force winds still over 24 hours away,
opted to maintain the storm force watch and allow the next
forecast to monitor trends, especially for the start and end
time of the storm force winds, which are expected to end across
the Illinois nearshore waters earlier, perhaps Monday morning,
while continuing a bit longer across northwest Indiana. Gale
force winds are then expected to continue into Monday evening.

Freezing spray will also be possible early Monday morning and
continue into Monday night as air temperatures are expected to
be in the lower 20s and possibly into the teens. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory from 6 PM Sunday to 6 PM CST Monday for ILZ003-
     ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
     ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-
     ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Wind Advisory from 6 PM CST /7 PM EST/ Sunday to 6 PM CST /7
    PM EST/ Monday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Storm Watch from Sunday evening through Monday morning for
     Winthrop Harbor IL to Gary IN.

     Storm Watch from Sunday evening through Monday afternoon for
     Gary to Burns Harbor IN-Burns Harbor to Michigan City IN.

&&

$$

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